The coagulation phenomenon comprises a cascade of enzymatic reactions involving coagulation factors of which several are proteases comprising a serine in their active site. The final step is the conversion of soluble fibrinogen into fibrin filaments which surround circulating cells in their meshes. Coagulation factors are denoted by numbers ranging from I to XIII. With the exception of factor XIII, which is involved in the final step of coagulation, the other factors are involved in reverse order of their numbering; thus, factor XII initiates coagulation and factor I ends it. Each factor exists in the form of an inactive precursor and in activated form, indicated by the letter a.
Coagulation involves two pathways, one intrinsic, the other extrinsic, resulting in a common final pathway. The combination of the two mechanisms ensures the formation of a solid and flexible blood clot, which withstands blood pressure while at the same time guaranteeing sufficient mobility. Under the action of thrombin, fibrinogen undergoes chemical modifications which result in the formation of fibrin. Fibrin is necessary for clot formation.
The intrinsic pathway comprises the factors present in the circulation and the coagulation process begins right within the blood vessel. The extrinsic pathway, for its part, involves tissue factors that are not normally present in the circulation and that are released during vascular damage. It is when this pathway is activated that a chain reaction occurs, during which an activated coagulation factor triggers the activation of the subsequent coagulation factor. This pathway involves the intervention of factor VII (FVII) present in the plasma. Activated factor VII, also called proconvertin, is one of the factors, having a molecular weight of approximately 50 kDa, involved in the blood coagulation mechanism. It is a glycoprotein of the serine protease family, the synthesis of which in activated form is vitamin K-dependent. In order to initiate the coagulation cascade, FVII must be activated to FVIIa. FVIIa alone (not complexed) has a weak proteolytic activity. Then, once activated, FVIIa complexes with tissue factor (TF), a phospholipid-associated protein, which is released during the vascular damage. The FVIIa-TF complex subsequently converts factor X to factor Xa in the presence of calcium ions. This complex also acts on the activation of FIX to FIXa, thus catalysing the intrinsic pathway. Factors IXa and Xa in return activate the activated factor VII. Factor Xa complexed with activated factor FV and with prothrombinase, converts prothrombin to thrombin. Thrombin then acts on fibrinogen in order to convert it to fibrin and also allows the activation of FVIIIa and of FVa from, respectively, FVIII and FV. Thrombin makes it possible, for its part, when it is in the presence of calcium, to activate factor XIIIa responsible for consolidation of the fibrin clot. Nevertheless, when a coagulation factor is lacking, the cascade of reactions is interrupted or defective and the term abnormal coagulation is then applied.
Activated factor VII acts locally in the presence of tissue factor released after tissue damage causing haemorrhage, even in the absence of factor VIII or IX. For this reason, factor VII, preferably in activated form, has been used for a long time for the treatment of certain blood coagulation disorders manifested by bleeding. The factor is involved in many pathological conditions, such as haemophilia type A or B, in which the patients exhibit factor VIII or IX inhibitors, acquired haemophilia or congenital factor VII deficiency, and as a product for preventing haemorrhages that can occur during surgical operations.
At the current time, a medicament available on the market for the treatment of these patients suffering from haemophilia or from congenital factor VII deficiency is known. It is NovoSeven®, authorized on the European market since 1996 and authorized on the American market in 1999, produced by the Danish company NovoNordisk. NovoSeven® is a medicament of which the active ingredient is eptacog alfa (recombinant human activated coagulation factor VII produced by genetic engineering from BHK baby hamster kidney cells). This product also contains sodium chloride (2.92 g/l), calcium chloride dihydrate (1.47 g/l), glycylglycine (1.32 g/l), polysorbate 80 (0.07 g/l) and mannitol (30 g/l).
A variant of NovoSeven also exists, called NovoSeven® RT, which enables storage of the product at room temperature (25° C.). This second product consists of sodium chloride (2.92 g/l), calcium chloride dihydrate (1.47 g/l), glycylglycine (1.32 g/l), polysorbate 80 (0.07 g/l), mannitol (25 g/l), and hydrochloric acid and sodium hydroxide for adjusting the pH, and also contains sucrose (10 g/l) and methionine (0.5 g/l) (used as antioxidant). The returning of this product to solution requires water for injection, but also histidine. NovoSeven® RT was authorized on the European and American markets in 2008.
The main therapeutic indication for recombinant FVIIa (rFVIIa) concerns the treatment of spontaneous or surgical bleeding in type A haemophiliacs having developed anti-factor VIII antibodies and type B haemophiliacs having developed anti-factor IX antibodies. In Europe, it is also indicated for use in patients with a congenital FVII deficiency and in patients suffering from Glanzmann's thrombasthenia. In addition, numerous publications report the efficiency of rFVIIa in controlling haemorrhage during surgical procedures, in patients who have neither a congenital deficiency in a coagulation factor nor thrombasthenia.
An article by Nedergaard et al., 2008 [Nedergaard H. et al., In vitro stability of lyophilized and reconstituted recombinant activated factor VII formulated for storage at room temperature, Clinical Therapeutics, Vol 30, No. 7, p 1309-1315, 2008] teaches that NovoSeven® RT remains stable for a period of 24 months at 25° C., 12 months at 30° C., 6 months at 40° C. and 12 hours at 50° C. and 60° C. in its lyophilized form. Furthermore, this product is stable only for six hours after liquid reconstitution thereof, and consequently it is recommended to perform the injection within three hours following reconstitution. This product therefore exhibits, by virtue of this stability, handling difficulties and constraints in terms of administration times.
Patent EP 1 210 361 discloses the advantage of using glycylglycine for stabilizing a lyophilized composition of activated factor VII.
Patent application WO 2004/000347 proposes various other stabilizing agents.
The publication by Soenderkaer S. et al., 2004 [Soenderkaer S. et al., Effects of sucrose on rFVIIa aggregation and methionine oxidation, European Journal of Pharmaceutical Sciences, Vol 21, p 597-606, 2004] describes sucrose as an essential excipient for stabilization against aggregation and heat denaturation of activated factor VII. According to this teaching, sucrose enables the protein to retain its native form in aqueous solution, by excluding sugars from the surface of the proteins, which makes it possible to increase the chemical potential of the molecule. Consequently, and by reducing its surface area, the protein remains in a compact conformation. The presence of sucrose as an excipient makes it possible to stabilize the activated factor VII in its lyophilized form.
However, the presence of sucrose leads to the induction of antioxidant compounds in the formulation, resulting in technical and regulatory constraints associated with the addition of compounds of this type.
There is therefore today a real need to develop medicaments containing factor VII which are free of antioxidants, chemically and physically stable at room temperature, and easy for patients to use, in particular patients suffering from haemophilia or from congenital factor VII deficiency.